entrenchment vs supply depot

entrenchment

noun
  • A fortification constructed of trenches 

  • The process of entrenching or something which entrenches 

supply depot

noun
  • A facility utilized by armies to store battlefield supplies temporarily on or near the front lines until they can be distributed to army units. 

How often have the words entrenchment and supply depot occurred in a corpus of books? (source: Google Ngram Viewer )